Radio receivers are typically designed to receive electromagnetic signals in the radio frequency (RF) portion of the electromagnetic spectrum. Generally a desired radio signal is intercepted by a radio antenna and propagated along with other undesired signals to electronic circuits within the radio. Additional undesired radio signals, including for example intermodulation (IM) products are created by interactions of both desired and undesired radio signals from both the antenna and within the radio. The undesired signals (e.g. a blocker signal at some frequency offset from the desired signal) can be relatively strong compared to the signal strength of the desired signal. Receivers of the prior art can be overwhelmed by such blocker signals and as a consequence can fail to properly receive and/or fail to properly process (e.g. demodulate) a desired signal.
There exist well known metrics in the radio industry which can be used to judge receiver performance in the presence of unwanted interfering signals. For example input saturation affects can be described by the input gain compression point (ICP1) measurement or specification. Intermodulation effects are described in part by a third input intercept point (IIP3) measurement or specification. While such measurements as the ICP1 and IIP3 parameters describe in part conditions under which a radio continues to operate properly, there has been little success in designing a radio receiver that can work in the presence of large blacker signals whose voltage magnitude is on the order of that of the circuit voltage supply rail.
What is needed, therefore, is a radio receiver circuit topology which enables a radio receiver to correctly receive and process a desired radio signal in the presence of one or more interfering signals.